1. Field of the Invention
The invention in general relates to acoustic detection systems and more particularly to one utilizing fiber optics.
2. Description of the Prior Art
A fiber optic sonar system is based on the principle that acoustic waves travelling in a medium vary the index of refraction of the medium and therefor the presence of acoustic waves may be detected by an optical interferometer.
The system generally includes two light conducting optical fibers one of which is exposed to the acoustical waves and the other of which is isolated therefrom. A light beam transmitted into the two fibers by a laser light source is modulated in the optical fiber exposed to the acoustical waves and the second beam, acoustically isolated, serves as a fixed reference beam. The modulated and unmodulated beams are combined by a beam splitter to form an interference pattern that is detected by a photodetector device resulting in an electrical signal at the acoustic frequency.
The present invention utilizes these fiber optic principles in a sonar system which is able to detect the actual movement of a target into or out of an area under surveillance.